VJC 2023 H2 9744 P2 Ans

1 Victoria Junior College Biology Department 2023 Prelims H2 Paper 2 – Proposed Answers Marking abbreviations: A: Accept, R: Reject, AW: alternative wording, AVP: Any valid point, NAQ: not answering question, ECF: error carried forward 1 The cell surface membrane regulates the movement of different substances via different mechanisms. Table 1.1 shows the results from an investigation to determine how two different drugs A and B enter animal cells. Table 1.1 concentration of drug A in container / arbitrary units concentration of drug A inside the cells after 5 minutes / arbitrary units concentration of drug B in container / arbitrary units concentration of drug B inside the cells after 5 minutes / arbitrary units 0 0 0 0 5 5 5 4 10 10 10 7 15 15 15 11 20 19 20 13 25 24 25 13 Cells which did not contain either drug were placed into separate containers. Different concentrations of each drug were added and after 5 minutes, the drug concentration in the cells was measured. (a) Based on the data shown in Table 1.1, (i) state the chemical nature of drugs A and B [1] • A is lipid soluble/hydrophobic whereas B is polar/hydrophilic; (ii) explain the difference between the transport of drugs A and B. [3] • Data to support differences: Concentration of the drug A inside the cells matches/similar to the external concentration while for drug B, as external concentration increases, the internal concentration also increases but reaches a plateau; • Drug A enters by simple diffusion whereas B enters via facilitated diffusion; OR Drug A diffuses across the phospholipid bilayer/ hydrophobic core of cell membrane into cell, but B requires carrier/ channel proteins to enter cell; • A: moves down concentration gradient from outside of the cell into the cell until equilibrium is reached; • B: (Idea of) the number of carrier/ channel proteins on cell membrane are fixed/ saturated;

2 (b) Viruses make use of certain properties of the cell membrane to facilitate its own release from the host cell. Fig. 1.1 shows such a process. (i) Explain clearly how the structure of the cell membrane facilitates this process. [3] • Phospholipid bilayer structure of the cell membrane provides fluidity / lateral movement within their own monolayer; • P hospholipids held by weak hydrophobic interactions between the hydrocarbon tails of the phospholipids; • allowing the cell surface membrane to change its shape / be pushed outwards – budding; • (idea of) allowing viral glycoproteins to be embedded in cell surface membrane as exit points; (ii) Contrast the process seen in Fig 1.1 with the process in which HIV virus enters the host cell. [2] Process shown in Fig 1.1 Process which HIV virus enters the host cells [Any 2 of the following] • Budding involving evagination of host cell surface membrane • Inv olves removal / loss of cell membrane; • Involves viral glycoproteins on cell